What Size Solar Panel To Charge 400ah Battery? + Calculator

You need about 500-600 watts of solar panels to fully charge a 12v 400ah lead-acid battery from 50% depth of discharge. And 800-1000 watts of solar panels to fully charge a 12v 400ah lithium (LiFePO4) battery from 100% depth of discharge in a day.

”What size solar panel do you need to charge 400ah lead-acid or lithium battery?” Use the calculator given below to find out.

Solar Panel Size Calculator For Battery

Battery Capacity (Amp-hours)
Ah
Battery Voltage
V
Battery Type
Charge Controller Type
Desired Charge Time (Peak sun hours)
hours

Note: If you already have a solar panel and want to know how long it will take to charge your battery, use this solar battery charge time calculator.

Calculator Assumptions: 

  • Lead-acid Battery Charge efficiency rate: 85%
  • AGM Battery Charge efficiency rate: 85%
  • Lithium (LiFePO4) Charge efficiency rate: 99%
  • PWM charge controller: 80% efficient
  • MPPT charge controller: 98% efficient
  • Solar Panels Efficiency during peak sun hours: 80% (meaning a 100 watt solar panel will produce 80 watts during peak sun hours, i’ll explain why…)
  • Charge controller is the only load connected with the battery

How To Use The Calculator?

Enter the following info into the calculator ( located at the top of this page )

  • Battery Capacity: Enter your battery capacity in amp-hours (Ah). in this case it’ll be 400
  • Battery Volts: is this a 12v, 24v, or 48v battery? ( if you connect multiple batteries in series their voltage will ad up but the current will stay the same, if you connect in parallel the voltage will stay the same but amps will add up )
  • Battery Type: Select the battery type, is this a lead-acid, AGM, or lithium-ion (LiFePO4) battery?
  • Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. for half discharged battery you’d enter 50, (if the battery is fully discharged which you can achieve on lithium battery, ENTER 100)
  • Charge Controller Type: Are you using a PWM or MPPT charge controller to charge the battery? 
  • Desired Charge time (in peak sun hours): How fast would you like to charge your battery or how many peak sun hours your location receives? (keep reading i’ll explain how you can calculate the number of peak sun hours)  

After entering the information, click “Calculate” button to find the required size for a 200ah battery. 

Example 

Suppose you have a 24v 400ah lead-acid battery with 50% depth of discharge and an MPPT charge controller. You want to recharge your battery in one day (during summer days) and your location receives 6 hours of peak sunlight 

What Size Solar Panel To Charge 400ah Battery
Screenshot from the calculator: What size solar panel to charge 400ah battery?

You’d need about 1100 watts of solar panels to fully charge a 24v 400ah lead-acid battery from 50% depth of discharge in 6 peak sun hours using an MPPT charge controller.

Read the below post to find out how fast you can charge your battery.

Related Post: Guide: Maximum Charging Current & Voltage For 12v Battery

What Are Peak Sun Hours?

Before explaining peak sun hours and why to use them, first, let’s see how solar panels are rated.

“ Solar panels are designed to produce their rated wattage output under standard test conditions – STC ”

STC includes: 

  • 1000 watts per meter square (1kw/m2) of sunlight intensity hitting the solar panels directly
  • 25oC temperature 

So to calculate the sunlight intensity we use peak sun hour as a reference. 

  • 1 peak sun hour = Average of 1kw/meter2 of sunlight intensity for one hour.

This number will depend on the location to location. To calculate how many peak sun hours your city receives use this PVwatt solar calculator.

Step 1: Enter your full address of just a city name & Click GO

Step 2: Click on results

How many peak sun hours in florida?

Now you’d be able to see the total amount of solar radiation your location receives per day (from month to month)

Note! it would have to place my solar panels all day long under sunlight to get those total solar radiations per day. 

Average Solar Panel Output?

In the real world on average you’d only receive about 70-80% of the rated output from your solar panels in peak sun hours. This is the average output that i receive from my 200-watt solar panels.

20-30% power losses will be due to fluctuations in the weather conditions, power losses in wiring, and charge controller inefficiency (especially if you’re using a PWM type) which I’ll cover in a bit.

To get the maximum output from your solar panels follow these points

  • Clean your solar panels from time to time
  • Use an MPPT charge controller
  • Choose the right size wire for your solar panels
  • Place your solar panels at the right title angle

Must Read: Solar Panel Output Calculator + how to get the maximum output from your solar panels

What Size Solar Panel To Charge 400ah Battery?

Here’s a chart on what size solar panel you’d need to charge your 12v, 24v, or 48v 400ah battery in desired peak sun hours.

12v 400ah Battery

Charge TimeEst. Solar Panel Size For 12v 400ah Lead-acid BatteryEst. Solar Panel Size For 12v 400ah Lithium Battery
4 peak sun hours830 watts1.45 kWh
5 peak sun hours660 watts1.2 kWh
6 peak sun hours550 watts960 watts
7 peak sun hours470 watts830 watts
10 peak sun hours330 watts580 watts
15 peak sun hours220 watts390 watts
20 peak sun hours165 watts290 watts

Table: what size solar panel to charge 12v 400ah lead-acid or lithium (LiFePO4) battery

Summary

  • You’d need around 660 watts of solar panels to charge a 12v 400ah lead-acid from 50% depth of discharge in 5 peak sun hours and 1.2kWh of solar panels for lithium (LiFePO4) battery from 100% depth of discharge with an MPPT charge controller

24v 400ah Battery

Charge TimeEst. Solar Panel Size For 24v 400ah Lead-acid BatteryEst. Solar Panel Size For 24v 400ah Lithium Battery
4 peak sun hours1.65 kWh2.9 kWh
5 peak sun hours1.32 kWh2.3 kWh
6 peak sun hours1.1 kWh1.9 kWh
7 peak sun hours940 watts1.6 kWh
10 peak sun hours660 watts1.16 kWh
15 peak sun hours440 watts780 watts
20 peak sun hours330 watts580 watts

Table: what size solar panel to charge 24v 400ah lead-acid or lithium (LiFePO4) battery

Summary

  • You’d need around 1.32 kWh of solar panels to charge a 24v 400ah lead-acid from 50% depth of discharge in 5 peak sun hours and 2.3 kWh of solar panels for lithium (LiFePO4) battery from 100% depth of discharge with an MPPT charge controller

48v 400ah Battery

Charge TimeEst. Solar Panel Size For 48v 400ah Lead-acid BatteryEst. Solar Panel Size For 48v 400ah Lithium Battery
4 peak sun hours3.3 kWh5.8 kWh
5 peak sun hours2.65 kWh4.65 kWh
6 peak sun hours2.2 kWh3.87 kWh
7 peak sun hours1.9 kWh3.3 kWh
10 peak sun hours1.3 kWh2.33 kWh
15 peak sun hours880 watts1.55 kWh
20 peak sun hours660 watts1.16 kWh

Table: what size solar panel to charge 48v 400ah lead-acid or lithium (LiFePO4) battery

Summary

  • You’d need around 2.65 kWh of solar panels to charge a 48v 400ah lead-acid from 50% depth of discharge in 5 peak sun hours and 4.65 kWh of solar panels for lithium (LiFePO4) battery from 100% depth of discharge with an MPPT charge controller

What Size Charge Controller Do I Need To Charge The Battery?

The job of the charge controller is to regulate the voltage coming from the solar panels to safely charge the battery and prevent the battery to be overcharged.

To select the right size charge controller according to your solar panel size. Follow these 2 steps

  1. Divide the solar panel rated wattage by battery volts (e.g by 12 for 12v battery and so on…)
  2. Now add an extra 25% to the result value to keep the system safe in case of any fluctuations.
  3. Now the value will be the size of charge controller you’d need with your particular solar panel size to charge the battery.

For Example

let’s suppose you have a 100-watt solar panel and a 12v battery. the calculation will look like this.

100 / 12 = 8.33A
8.33 + 25% or 8.33 * 1.25 = 10.4 A

you’d need a 10A charge controller with a 100-watt solar panel to charge a 12v battery.

PWM Vs MPPT

– PWM Charge Controller

will only decrease the voltage coming from the solar panels and will not increase the amps (current).

which as a result will cause power losses and which makes the PWM charge controllers 20-30% less efficient.

The formula to power is… ( Watts = amps * volts )

Remember: a 12v solar panel will produce about 18 volts under direct sunlight conditions… and the amps will be lower.

Note! If you’re using an PWM charge controller the voltage of solar panel and battery should be the same. ( eg. 12v solar panel for 12v battery and 24v solar panel to charge a 24v battery ). Otherwise you’ll experience a huge power loss. If you have different voltage solar panels and battery then use an MPPT charge controller.

– MPPT Charge Controller

An MPPT charge controller will not only decrease the voltage coming from the solar panel to charge the battery but will also increase the amps to cover up the losses.

which makes them 98-99% more efficient than a PWM charge controller.

Pro Tip: if your solar panel system is higher then 100 watts then i would suggest using an MPPT charge controller.

Related Post: How Many Watts Can A Charge Controller Handle?

Solar Wiring Size Guide

wire gauge chart

To calculate the cable size from solar panel to charge controller and from the charge controller to the battery bank use this formula (amps = watts/volts) to calculate the number of amps your cable would have to handle

For Example, if you’re using a 600 watt of solar panels to charge your 12v 400ah battery you’d need 5 gauge size wire (600 watt/12v = 50 amps)

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I hope this short guide was helpful to you. still, have any confusion? LEAVE A COMMENT or contact us. Thank You!

I'm an experienced Sales Consultant with a demonstrated history of working in the renewables and environment industry. Skilled in Photography, Customer Service, and Sales.

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